When standardized weed and grass pollen extracts were licensed they were arbitrarily assigned 100,00 AU/ml if they were equipotent to the reference. With the introduction of the ID50EAL method, Bioequivalent Allergy Units are currently assigned based on skin test potency determined in highly skin reactive rhinitis subjects. Using the ID50AEAL method, proposed FDA reference preparations of giant ragweed and Bermuda grass were evaluated clinically. In each reference the mean D50 fell between 11-12.9, indicating they should be assigned 10,000 BAU/ml rather then the 100,000 AU/ml arbitrarily assigned. The Bermuda grass reference was also evaluated in another region of the U.S. to determine whether the CBER estimate was replaceble. When sugjects equal in reactivity were selected in Nashville, no significant difference with the Nashville D50 estimate with respect to the CBERmuda D50 estimate was found confirming the assignment of 10,000 BAU/ml to the Bermuda reference. When standardized short ragweed extracts were licensed and labelled in Allergy Units, they were arbitrarily assigned 100,000 AU/ml, if they contained between 200 to 400 Amb a 1 units/ml. Estimation of the D50 of standardized short ragweed extracts at 250, 300, 315, 500 and 900 Amb a 1 u/ml indicated that extracts with Amb a 1 contents of 250 to 450 u/ml warranted assignment of 100,000 BAU/ml.